Crosslinkable compositions which comprise an organopolysiloxane containing Si-bonded vinyl groups, an organopolysiloxane containing Si-bonded hydrogen atoms and a catalyst which promotes addition of Si-bonded hydrogen onto an aliphatic double bond, are known from U.S. Pat. No. 3,445,420, published May 20, 1969, (G. J. Kookootsedes et al., Dow Corning Corp.) and GB-A 1,374,792, published Nov. 20, 1974, (J. A. Colquhoun et al., Dow Corning Ltd.).
U.S. Pat. No. 4,347,346, published Aug. 31, 1982, and U.S. Pat. No. 4,476,166, published Oct. 9, 1984, (R. P. Eckberg, General Electric Co.) and U.S. Pat. No. 4,504,645, published Mar. 12, 1985, (K. C. Melancon, Minnesota Mining and Manufacturing Co.) disclose that in addition to an organopolysiloxane having Si-bonded vinyl groups, an organopolysiloxane having other alkenyl groups, such as Si-bonded allyl, butenyl or pentenyl groups, may be used in crosslinkable compositions for the production of non-stick coatings.
Crosslinkable compositions which are used for the production of non-stick coatings and comprise an organopolysiloxane containing higher alkenyl groups, such as Si-bonded hexenyl groups, are known from U.S. Pat. No. 4,609,574, published Sep. 2, 1986 (J. R. Keryk et al., Dow Corning Corp.). The organopolysiloxanes containing higher alkenyl groups are usually prepared in a multi-stage process from the corresponding silanes by reacting an .alpha.,.OMEGA.-diene in a large excess with a silane having an Si-bonded hydrogen atom and thereafter hydrolyzing and equilibrating these silanes with organopolysiloxanes.
Therefore, it is an object of the present invention to provide siloxane copolymers which contain alkenyl groups. Another object of this invention is to prepare siloxane copolymers containing alkenyl groups in a simple process. Another object of the present invention is to provide a process for preparing siloxane copolymers in which more than one alkenyl group is added to one Si atom. Still another object of the present invention is to prepare siloxane copolymers which crosslink rapidly with organopolysiloxanes containing Si-bonded hydrogen atoms in the presence of a catalyst which promotes the addition of Si-bonded hydrogen onto an aliphatic double bond. Furthermore, it is an object of the present invention to provide crosslinkable compositions which may be used in the production of non-stick coatings.